Process of making molded conductors.



0. VAN BRUNT.

PROCESS OF MAKING MOLDED GONDUGTORS. APPLICATION FILED 111112.23, 1910.

1,017,483, Patented Feb. 13, 1912.

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5 of the binder.

UNITED STATES CHARLES VAN BRUN'I, 0F SCHENECTADY, NEW

YORK, ASSLGN OR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROCESS OF MAKING MOLDED CONDUCTORS.

Specification of Letters Patent.

Application filed March 23, .1910. Serial No. 551,157.

To all whom it may concern Be it known that a citizen of the United States, residing at Schenectady, county of Schenectady, State 5 of New York, have invented certain new and useful Improvements in Processes of Making Molded Conductors, of which the following is a specification.

My invention relates to the production of molded articles such as brushes for dynamo electric machines, electrodes, packing rings, contacts, and the like, from carbonaceous material, and particularly to molded articles made by compacting carbonaceous material with a carbonizable binder, such as a heavy hydrocarbon. Y

In accordance. with my invention, sulfur is added to the raw carbonaceous material. The sulfur appears to react upon heating with the hydrocarbon binder such as coal tar pitch, or petroleum pitch, with the formation of gaseous compounds, such as hydro gen sulfid, which by removing hydrogen from the pitch increase the total amount of carbon residue when the molded articles are fired, and thus increases the density, strength and conductivity of the final product.

The accompanying drawing shows a carbon brush for dynamo electric machines as illustrative of the class of articles to which my invention is applicable.

My invent-ion is not limited to any particular mixture of carbonaceous materials, or to any particular process for mixing, or molding these materials. For the sake of illustration, however, I will describe a method for introducing the sulfur into the carbonaceous mixture.

In accordance therewith, a carbonaceous material such as powdered graphite, either with or without an admixture of powdered coke or lamp black, according to the nature of molded article desired, is mixed with a suitable amount of pitch and sulfur-and ground together in a liquid solvent for the binder, such as benzol. The amount of binder is determined by the quality and composition of the binder and by the geueral nature of the ingredients of the mixture. When using a hard pitch binder, about 30% of binder is ordinarily employed. The proportion of sulfur to the binder is in turn determined largely by the character It may .vary within wide I, CHARLES VAN BRUNT,

limits, for example, all the way between 5 and With a hard coal-tar pitch- I have used an amount of sulfur corresponding to 17% of the total amount of binder with good success. The grinding treatment mass. Thesolvent is then driven off, by distillation. The caked residue is again pulverized and is then ready for molding into desired form, as If desired the carbonaceous materials and the sulfur may be mixed by simply grinding together while dry. The molded articles are baked at a temperature of about 400500 C. to carbonize and set the binder. During the initial stages of the baking treatment the sulfur binder to eliminate hydrogen from the hydrocarbon. When the carbonizing temperature is approached, the binder contains a larger proportion of carbon than it is the case when sulfur is not used, in other Words, it has been convertedinto a heavier, or lower hydrocarbon. This heavier hydrocarbon appears to leave a greater residue of coke upon carbonizing. A certain percentage of the hydrogen having been removed by the sulfur, when the compound breaks up and carbonizes yielding volatilizable hydrocarbons, and coke, the decreased proportion of hydrogen carries away less carbon by distillation from the compound as volatilized hydrocarbon, and more coke is left in the pores of the molded article, making it stronger and denser. I do not wish to be limited, however, by the above explanation of what takes place, as my invention may be practiced'without reference to any theoretical considerations.

If desired, the carbon articles after baking to a temperature at which the binder is carbonized may be subsequently treated to still further raise their density as by impregnating with pitch followed by a second firing. The final firing ordinarily is carried on at a temperature approaching 1100 to 1200 C. The increased amount of coke pears to act not only as a filler to decrease the porosity of the product, but it appears to cause increased shrinkage during the firing of the article as a whole. In other Words, an increase of coke residue from the binder has a two-fold effect, 'it fills up residue apin the liquid solvent thoroughly distributes the binder and the sulfur throughout the I by pressmg, or squirting.

Patented Feb. 13, 1912.

reacts with the hydrocarbon the voids more completely, and during the amples will illustrate, which give the density, the resistance in ohms per inch cube and the tensile strength in pounds per square inch of a brush for a dynamo electric machine consisting of graphite formed with 30% coal-tar pitch binder and containing sulfur to the amount of 5% of the total mass of mixture. The brushes were baked in each case to a temperature of about 500, then impregnated with pitch and finally fired to a temperature of about 1200 C.

Before impregnation.

- Resist- Tensile Denmy ance. Strength.

' Ohms. Pounds. Without sulfur 1. 41 00085 1, 550 With 5% 1. 59 .00059 2, 680

After impregnation.

- Resist- Tensile ance. strength.

Ohms. Pounds; Without sulfur 1.56 00070 2, 410 With 5% 1.67 .00058 ,41

What I claim as new and desire to secure by Letters Patent of the United States, 1s,

1. The process which consists in mixing carbonaceous material, a carbonizable binder and sulfur, compacting said mixture, and firing to a temperature sufiicient to carbonize said binder. x p

2. The process of forming articles from carbonaceous material, which consists in mixing said material with a heavy hydrocarbon and sulfur, pressing said mixture into predetermined form, and heating at an elevated temperature to carboni'ze said hydrocarbon.

3. The process of increasing the density of a molded conductor into whose formation carbonizable hydrocarbon compounds enter, which consists in adding sulfur to the raw mixture and firing to a temperature sufficient to carbonize said hydrocarbon compounds.

4. The process which consists in mixing carbonaceous material and pitch, with sulfur, compacting said mixture and firing to a temperature in the neighborhood of 4.00 to 500 C to carbonize the pitch.

In witness whereof, I have hereunto set my hand this 21st day of March, 1910.

CHARLES VAN BRUNT.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD. 

